I’m a few weeks into a winter of swimming and a few of my go to sets which I’ve been repeating most weeks are (all with 800m WU and drills and a bit of easy swimming as a cool down)
- 4x(4x100m 15 sec RI into 1x200m Pull + Paddles 30sec RI)
- 400m; 2x50 kick;300m; 2x50m kick; 200m; 2x50m kick; 100m; 2x50m kick
- Pyramid of 25m; 50m; 75m; 100m; 125m; 150m; 175m; 200m and back down again
- 15x (100m swim; 50m Pull 15 sec RI)
If I’m short of time or I’m swimming after a hard run or ride I’ll jump in and do 20 or 25 x 100m Pull to give my legs a rest.
That’s just a few sets I’ve fallen into doing but there are loads of other sets you could do as well obviously. I agree with @JoeX - I find that 3 swims a week is good to maintain but more than that to improve - for me anyway. I’ve used the Swim Smooth plans before which are pretty good but haven’t felt the need to subscribe for a while now.